The present invention relates to systems and methods for adapting program codes for execution on different computer systems and more particularly to systems and methods for translating codes based on a first instruction set to codes based on a relatively reduced instruction set while preserving instruction granularity.
In the early years of computer programming, instructions for computer programs were generated at the microcode level. With the development and growth of software engineering, more tasks were combined in single complex instructions executable by computers having a hardware architecture designed for the instruction complexity.
Increasing instruction complexity generally provided increasing price/performance benefits in the developing environment of computer hardware costs and performance capabilities. As a result, complex instruction set codes (CISC) became widely accepted.
With increased instruction complexity, however, it has become more difficult to design system hardware for higher execution speed. Instead, a reduced instruction set code (RISC), coupled with correlated RISC computer hardware architecture, has gained acceptance as a mechanism to lead to significantly improved system price/performance.
A RISC system generally employs simpler basic instructions to direct desired operations. A single RISC instruction normally specifies a single operation with at most a single memory access. Further, a RISC system normally provides a register for each basic instruction. The instructions in a RISC instruction set are thus still at a higher level than microcode.
In the typical CISC system, a single instruction may specify a complex sequence of operations and it may make many direct accesses to memory. Thus, operations performed by a CISC instruction may require several RISC instructions.
A RISC system is generally designed with optimized hardware and software tradeoffs that provide faster system operation, better overall system performance and lower system cost relative to available hardware cost and performance capability.
One obstacle to conversion from CISC systems to RISC systems is the existence of large software libraries which have been developed for CISC systems and which are not generally available for RISC systems. When a computer system user chooses to acquire a new computer system, one of the user's major considerations is whether the user's library of application programs can be used or converted for use on the new computer system, and what the cost of replacing that library would be. Thus, for computer system users who wish to achieve better price/performance through RISC computer systems, it is highly important that an economic and effective mechanism be provided for adapting, or "migrating" the user's library of application programs for execution on the RISC computer system.
Several choices are available to the user for program migration. Recompiling or recoding can be employed, but these techniques are typically used for migrating programs written in a high level language such as FORTRAN which either have no detailed machine dependencies or which have any existing machine dependencies removed by manual programming modifications. Further, in recompiling or recoding, the user typically bears all responsibility for program modification and program behavioral guarantees.
Alternatively, interpretation procedures can be used, but the penalty for this approach typically is substantially reduced program performance. More particularly, interpretation procedures are software programs that run on one computer and read a stream of subject instructions (which may well be instructions for a different type of computer) as data, and for each subject instruction perform the indicated operation. Such procedures typically execute 10 to 100 machine instructions on the one computer to interpret a single subject instruction. Thus, interpretation procedures provide substantially reduced program performance, compared to direct execution of functionally-equivalent code on the one computer.
The most effective and efficient migration, however, involves code translation. In code translation, each instruction from an existing program is translated into one or more instructions in the language of the destination machine. Accordingly, a translation of CISC programs to RISC programs, or more generally a program translation in which the translated code has a relatively reduced instruction set, requires "multiple" or "many" instructions in the translated code for each instruction in the code being translated. However, in making "one to many" or CISC-to-RISC code translations, it is generally difficult to preserve many of the instructions behavior guarantees originally provided with the CISC or other relatively complex code.
One normal CISC guarantee that presents some difficulty in translation is the requirement that no other CISC instruction or portion thereof can be executed between the beginning and ending of a single CISC instruction. Accordingly, in translating CISC to RISC it is essential that instruction wholeness or granularity be preserved. Preservation of instruction granularity requires that state or memory atomicity be preserved. Thus, either all memory accesses in an instruction must appear to happen or none must appear to happen in the translated code.
To preserve instruction granularity in the translation process, assurance must be provided that each set, or "grounds", of translated instructions corresponding to each more complex instruction will execute to produce the same result that the corresponding more complex instruction would have produced. This must be true even though asynchronous events may occur during execution of any of the "granules" of simpler translated instructions.
Accordingly, the present invention is directed to a mechanism and process for producing and executing translated codes from existing codes with preservation of instruction granularity thereby enabling computer system price/performance upgrades to be realized while preserving application code investments.